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/*-------------------------------------------------------------------------
*
* supportnodes.h
* Definitions for planner support functions.
*
* This file defines the API for "planner support functions", which
* are SQL functions (normally written in C) that can be attached to
* another "target" function to give the system additional knowledge
* about the target function. All the current capabilities have to do
* with planning queries that use the target function, though it is
* possible that future extensions will add functionality to be invoked
* by the parser or executor.
*
* A support function must have the SQL signature
* supportfn(internal) returns internal
* The argument is a pointer to one of the Node types defined in this file.
* The result is usually also a Node pointer, though its type depends on
* which capability is being invoked. In all cases, a NULL pointer result
* (that's PG_RETURN_POINTER(NULL), not PG_RETURN_NULL()) indicates that
* the support function cannot do anything useful for the given request.
* Support functions must return a NULL pointer, not fail, if they do not
* recognize the request node type or cannot handle the given case; this
* allows for future extensions of the set of request cases.
*
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/nodes/supportnodes.h
*
*-------------------------------------------------------------------------
*/
#ifndef SUPPORTNODES_H
#define SUPPORTNODES_H
#include "nodes/primnodes.h"
struct PlannerInfo; /* avoid including relation.h here */
/*
* The Simplify request allows the support function to perform plan-time
* simplification of a call to its target function. For example, a varchar
* length coercion that does not decrease the allowed length of its argument
* could be replaced by a RelabelType node, or "x + 0" could be replaced by
* "x". This is invoked during the planner's constant-folding pass, so the
* function's arguments can be presumed already simplified.
*
* The planner's PlannerInfo "root" is typically not needed, but can be
* consulted if it's necessary to obtain info about Vars present in
* the given node tree. Beware that root could be NULL in some usages.
*
* "fcall" will be a FuncExpr invoking the support function's target
* function. (This is true even if the original parsetree node was an
* operator call; a FuncExpr is synthesized for this purpose.)
*
* The result should be a semantically-equivalent transformed node tree,
* or NULL if no simplification could be performed. Do *not* return or
* modify *fcall, as it isn't really a separately allocated Node. But
* it's okay to use fcall->args, or parts of it, in the result tree.
*/
typedef struct SupportRequestSimplify
{
NodeTag type;
struct PlannerInfo *root; /* Planner's infrastructure */
FuncExpr *fcall; /* Function call to be simplified */
} SupportRequestSimplify;
#endif /* SUPPORTNODES_H */
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